I read reviews from both review sites and users to get a general feel for how satisfied folks are with a camera, lens or accessory, and to understand any common issues. With a camera, for instance, it's useful to know if the firmware user interface is well structured and the control layout works well, how good the battery life is, what the buffer clearing times are like etc. With lenses, it's useful to know if purple fringing or other aberrations are significant, or if flare is a big problem etc.
Beyond that, I've learned that I'm the only reviewer I can fully trust, so I need to use the item myself (which generally means buying it). That's not a criticism of others, but recognition that individual expectations, preferences, measurement criteria and motivations all feature strongly in how someone reviews and rates a particular item. I'm as unique as anyone else in that respect, but in my case I believe I'm pretty forgiving of equipment quirks and weaknesses compared to some. There isn't a DSLR or mirrorless camera I've used in the last 10 years that I couldn't get on with, whilst acknowledging that some are better than others in different aspects of performance and operation, and might require some adaptation in the ways I shoot. Same with lenses. I don't expect critical sharpness and perfect contrast wide open; I don't mind a bit of vignetting and a little distortion. I do like detail, but I don't mind applying a bit of sharpening and/or clarity in post to bring it out. If I'm fussy, it's in the overall rendering character of a lens - but I've never read a review that quantifies that in ways that fully match my personal likes.
So, I do find reviews useful to a point - i.e. to capture a general consensus on the item I'm interested in. But unless that consensus is overwhelmingly negative, I'm likely to base my purchasing decisions on a personal assessment of specs, features, manufacturer and price. Then, if I buy, I'll form my own opinion as I use the item. If, after using it for some time, I don't like it, I can sell it and recoup at least some of my investment, or simply chalk it down to experience